Abstract—Nowadays, in real power systems in most countries around the world, common measurement units and SCADA systems are used for data measurement and state estimation. Some Electricity Companies have installed and applied Phasor Measurement Units (PMUs) for system observability. Nevertheless, number of Phasor Measurement Units might be limited due to financial considerations and this limited number may be used together with common measuring systems. Thus, this paper provides a novel method for optimal placement of a limited number of phasor measurement units. Two main problem are discussed in this paper: one is placement of a limited number of phasor measurement units in case the units are less than the minimum number required for the system to be observable, and the other is placement of phasor measurement units in case the units are more than the minimum number required for the system to be observable. The first scheme takes into account the system observability in presence of Phasor Measurement Units, minimizing state estimation error and considering future supplementary plan, and also determining candidate buses for installing PMUs in future. While, the second one, takes into account maximizing measuring system reliability with an increase in redundancy of these measurement units and also determining candidate buses for installing PMUs in future. The proposed method has been simulated and analyzed on the IEEE standard 14 bus test system and the results show the efficiency of the method.

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